On Tue, 14 Aug 2001 21:56:20 -0400, Tom Rawson <[log in to unmask]> wrote:

>Can someone explain how "Last error:  Unavailable" happens and what "DSN"
>status means?

DNS=Domain Naming System  (a means of looking up addresses)  RFC1034 et al

DSN=Delivery Status Notification (failure/success of message delivery)
    RFC 1893/1894

"Last error:  Unavailable" means that the reason for the non-delivery or the
reason for the error report cannot be determined by LISTSERV, or has not been
correctly reported by the reporting server (msn.com).  The only way to know for
sure is to turn off LISTSERV's automatic error processing and for you to handle
all error msgs by hand.  Then you can see the original error msg sent by MSN and
what it says.  Normally this msg is not available because it is discarded by
LISTSERV after automatic proccessing.

I have have been doing extensive logging of msn.com traffic and I have
discovered that in all cases I have logged, the mail was successfully delivered
to and successfully acknowledged receipt by msn.com.  This means that after
accepting/receiving the mail they issue an error msg (for reasons still unknown)
using the error code 5.1.1 which means the user does not exist.

Properly functioning mail systems do not report real users as non-existing.
Obviously msn.com has continuing, but sporadic problems.  This is not under
LISTSERV's control.  It cannot know what is going on, and it can only respond as
best it can to error messages which say the user does not exist.  Yes, it can be
a burden to List Owners.  8-(